The present invention relates to a method for treating calcium borate ores to obtain useful boron-containing compounds. The invention also relates to the use of the resulting boron-containing compounds in the treatment of wood and other related wood-based products to protect such products against fungal attack, and against attack by subterranean termites and wood-boring insects such as powder-post beetles and carpenter ants. The invention further relates to the use of the boron-containing compounds to improve the flame retardancy of wood and wood products. Still further, the invention relates to the boron-containing compounds prepared by the inventive method for treating calcium borates.
Typically, wood and other cellulose products such as plywood and oriented strand board (OSB), are exposed to a wide range of weather and environmental conditions. During the useful lifetimes of such products, they may also become exposed to fungi, and/or they may become prey to various boring or wood-eating insects. Similarly, such products may become exposed to fire. Such exposure to fungi and insects hastens the degradation of the products. Exposure to fire or flames increases the risk of loss of life and property.
Methods and compositions for treating wood and cellulose products to provide at least some protection against such conditions are known in the art. In one such method, cellulose products are treated with a composition comprising sodium sulfate and ammonium pentaborate. This composition is generally obtained as a result of the reaction between sodium borates (borax) and ammonium sulfate in water. However, ammonium pentaborate is soluble in water. Therefore, the composition gradually leaches out of the treated wood or cellulose upon repeated exposure to outdoor moisture, such as rain.
Attempts have been made to minimize the leaching of the ammonium pentaborate by adding soluble calcium salts to the sodium sulfate/ammonium pentaborate composition, to obtain a second set of reaction products that is less prone to leaching out of the wood or wood products. However, results with the calcium salts have met with only limited success, as the post-addition of the calcium salts to the sodium sulfate/ammonium pentaborate composition generates insoluble calcium compounds and/or calcium borates, causing those insoluble products to precipitate out of the solution before application; Besides making the application more difficult, the above-described process can remove both calcium and borates from the composition to be applied to the wood, thereby decreasing the effectiveness of the composition. In order to avoid this condition a second set of reaction conditions would be required (secondary application to treated wood), thereby necessitating an additional treatment step to produce the desired products.
Calcium borate ores have previously been used as components in dry powder flame-retardant formulations. One such use was described in U.S. Pat. No. 3,865,760, to Pitts, et al., wherein the ore colemanite (or alternatively, the ores ulexite or pandermite) was used as a filler in a rubber and plastic dry powder formulation, alone or in combination with alumina trihydrate and calcium carbonate. In this formulation, high levels of unreacted dry colemanite were required in order to receive the desired flame-retardant effect.
Another such use was described in U.S. Pat. No. 4,076,580 to Panusch, et al. This patent discloses a process for producing flame-retardant cellulosic board, comprising treating the board with a xe2x80x9csynergistically actingxe2x80x9d composition consisting of alumina hydrate and ulexite. The combination requires loadings for flame retardation at high levels that sometimes interfered with the board properties.
Another use was described in U.S. Pat. No. 4,126,473 to Sobolev, et al. This patent discloses a three-component flame-retarding agent consisting of an xe2x80x9caluminousxe2x80x9d material, a boron-containing mineral such as colemanite or ulexite, and a xe2x80x9cco-synergistxe2x80x9d, namely a phosphate or sulfate-containing inorganic salt.
The use of the calcium borate ores colemanite and ulexite as a termite bait was described in U.S. Pat. No. 4,363,798 to D""Orazio. This patent describes a method for protecting a structure from termites, in which a composition comprising wood inoculated with brown rot fungus is used as an attractant. The wood is ground into sawdust, and mixed with a boron-containing toxicant, such as colemanite or ulexite. The termite bait or attractant is then placed in close proximity to a wood structure to be protected, so that termites will be attracted to the bait.
Attempts have also been made to obtain treatment solutions for either flame retardation or for the protection from wood decay fungi, termites and wood-boring insects using water-soluble sodium borates. However, since sodium borates are highly soluble in water, these products do not provide adequate resistance to leaching after the application to wood or wood products.
U.S. Pat. No. 4,873,084 to Sallay discloses an insecticidal composition utilizing ammonium pentaborate and a mildewcide. This patent discusses the insecticidal activity of ammonium pentaborates. Ammonium pentaborates are precursors to boric acid, which is formed during ingestion by the insect. The patent states that certain calcium and barium triborates act in a similar fashion to produce boric acid in vivo in insects, the boric acid being toxic to insects. In the process described in this patent, wood previously treated with ammonium pentaborate is secondarily treated with various barium and calcium salts to cause a chemical change to a less soluble barium and/or calcium borate product. A mildewcide such as Busan(copyright) or Tyrosan(copyright) is added to control wood-boring insects and wood decay fungi.
Another Sallay patent, namely U.S. Pat. No. 4,514,326, discloses a flame retardant composition comprising ammonium pentaborate, and an alkali and/or alkaline earth metal sulfate, sulfite, hydrophosphate, or mixtures of them. The reaction products are produced by heating an aqueous suspension of a metal tetraborate ore, and then reacting the resulting product with an animonium salt, such as ammonium sulfate. The disclosure states that the role of the by-product alkali salts is to increase the solubility of ammonium pentaborate in water. This patent does not address the problem of leaching away of soluble ammonium pentaborate that occurs with the use of water-soluble borates.
According to the present invention, leach-resistant compounds are produced from a reaction between naturally occurring calcium borate ores, such as colemanite, and an acid, such as acetic acid; and then treating the reaction products with ammonia. When applied to substrates such as wood and other cellulose products, the resultant compounds in a water-based solution provide enhanced flame retardancy protection, and provide enhanced protection against attack by wood decay fungi and insects.
The present invention utilizes naturally-occurring calcium borate ores that are extremely insoluible in water, and produces a compound or compounds that are soluble in water, thereby facilitating the preparation of the treatment solution, and the resulting application of the solution to the wood. The treated wood shows dramatic resistance to leaching by water after treatment and drying.
The invention advantageously utilizes the naturally bound calcium of the calcium borate ores to provide the increased resistance to leaching without the need of any post-treatment after the initial application. The calcium compound or compounds that are produced are placed in solution, and thereafter remain in solution. The compound or compounds so produced are apparently just as stable in solution as other borates similarly made from water-soluble sodium borates. Upon cold precipitation, the compounds may be reintroduced into solution upon heating.